The invention relates to hermetic packages that are commonly used to house semiconductor devices. One such device is known in the semiconductor industry as the ceramic side brazed dual in-line package. The package is of rectangular shape and has two rows of metal pins brazed to the sides thereof. A recess located in the body of the package receives a semiconductor device and means are provided for connecting the device bonding pads to metal pathways incorporated into the package. These pathways conductively communicate with the side brazed pins. The package is finally hermetically sealed by welding or soldering a closure lid over the package recess.
The package recess is ordinarily surrounded by a metallization ring that adheres to the ceramic. A solder preform is placed over the ring and a metal cap placed on top of the solder preform. The assembly is then heated to melt the solder which wets the metal lid and the metallization. Upon cooling the solder will secure the cap to the package. The metal cap is usually composed of a metal alloy of nickel, iron, cobalt and manganese known as Kovar which is compatible with the ceramic to which it is attached. To avoid corrosion problems the lid is ordinarily plated with nickel and then gold. The solder preform is composed of a gold-tin alloy which melts at about 280.degree. C. Alternatively, the lid can be composed of an environmentally resistant metal such as alloys of nickel, titanium, tantalum, niobium or tungsten or it may be composed of stainless steel. After the lid is soldered to the ceramic body it is imprinted with the device identification and other desired information such as the manufacturer and assembly date code.
The requirements of the metal lid are severe. The final surface must be noncorrodable and capable of taking and retaining the marking. It must be compatible with the ceramic body and solderable thereto, while maintaining a hermetic seal throughout thermal and mechanical cycling. The conflicting requirements has resulted in a rather expensive and somewhat unreliable closure seal. It would be desirable to reduce the cost and increase the reliability of the closure lid for the ceramic package.